Iontophoresis, according to Dorland's Illustrated Medical Dictionary, is defined to be "the introduction, by means of electric current, of ions of soluble salts into the tissues of the body for therapeutic purposes." Iontophoretic devices have been known since the early 1900's. British specification No. 410,009 (1934) describes an iontophoretic device which overcame one of the disadvantages of such early devices known to the art at that time, namely the requirement of a special low tension (low voltage) source of current which meant that the patient needed to be immobilized near such source. The device of that British specification was made by forming a galvanic cell from electrodes and the material containing the medicament or drug to be delivered transdermally. The galvanic cell produced the current necessary for iontophoretically delivering the medicament. This ambulatory device thus permitted iontophoretic drug delivery with substantially less interference with the patient's daily activities.
More recently, a number of United States patents have issued in the iontophoresis field, indicating a renewed interest in this mode of drug delivery. For example, U.S. Pat. No. 3,991,755 issued to Vernon et al.; U.S. Pat. No. 4,141,359 issued to Jacobsen et al.; U.S. Pat. No. 4,398,545 issued to Wilson; and U.S. Pat. No. 4,250,878 issued to Jacobsen disclose examples of iontophoretic devices and some applications thereof. The iontophoretic process has been found to be useful in the transdermal administration of medicants or drugs including lidocaine hydrochloride, hydrocortisone, fluoride, penicillin, dexamethasone sodium phosphate, insulin and many other drugs. Perhaps the most common use of iontophoresis is in diagnosing cystic fibrosis by delivering pilocarpine salts iontophoretically. The pilocarpine stimulates sweat production; the sweat is collected and analyzed for its chloride content to detect the presence of the disease.
In presently known iontophoretic devices, at least two electrodes are used. Both of these electrodes are disposed so as to be in intimate electrical contact with some portion of the skin of the body. One electrode, called the active or donor electrode, is the electrode from which the ionic substance, medicament, drug precursor or drug is delivered into the body by iontophoresis. The other electrode, called the counter or return electrode, serves to close the electrical circuit through the body. In conjunction with the patient's skin contacted by the electrodes, the circuit is completed by connection of the electrodes to a source of electrical energy, e.g., a battery. For example, if the ionic substance to be delivered into the body is positively charged (i.e., a cation), then the anode will be the active electrode and the cathode will serve to complete the circuit. If the ionic substance to be delivered is negatively charged (i.e., an anion), then the cathode will be the active electrode and the anode will be the counter electrode.
Alternatively, both the anode and cathode may be used to deliver drugs of opposite charge into the body. In such a case, both electrodes are considered to be active or donor electrodes. For example, the anode can deliver a positively charged ionic substance into the body while the cathode can deliver a negatively charged ionic substance into the body.
It is also known that iontophoretic delivery devices can be used to deliver an uncharged drug or agent into the body. This is accomplished by a process called electroosmosis. Electroosmosis is transdermal flux of a liquid solvent (e.g., the liquid solvent containing the uncharged drug or agent) which is induced by the presence of an electric field imposed across the skin by the donor electrode. As used herein, the terms "iontophoresis" and "iontophoretic" apply equally to electrically powered devices which deliver charged/ionic agents by iontophoresis as well as to electrically powered devices which deliver uncharged/nonionic agents by electroosmosis.
Furthermore, existing iontophoresis devices generally require a reservoir or source of the beneficial agent (which is preferably an ionized or ionizable agent or a precursor of such agent) to be iontophoretically delivered into the body. Examples of such reservoirs or sources of ionized or ionizable agents include a pouch as described in the previously mentioned Jacobsen U.S. Pat. No. 4,250,878, or a pre-formed gel body as described in Webster U.S. Pat. No. 4,382,529 and Ariura et al. U.S. Pat. No. 4,474,570. Such drug reservoirs are electrically connected to the anode or the cathode of an iontophoresis device to provide a fixed or renewable source of one or more desired agents.
More recently, iontophoretic delivery devices have been developed which utilize complex electrical circuits in order to perform a number of functions. These complex circuits include pulsing circuits for delivering a pulsed current, timing circuits for delivering drugs over predetermined timing and dosing regimens, feedback regulating circuits for delivering drugs in response to a sensed physical parameter, and polarity controlling circuits for periodically reversing the polarity of the electrodes. See for example, Tapper et al. U.S. Pat. No. 4,340,047; Lattin U.S. Pat. No. 4,456,012; Jacobsen U.S. Pat. No. 4,141,359; and Lattin et al. U.S. Pat. No. 4,406,658.
Very simple iontophoretic delivery circuits (e.g., a circuit consisting of only a DC power source electrically connected in series with the two electrodes) do not need a switch for disconnecting the power source from the circuit in order to prevent current drain from the power source. This is so because the electrodes, before placement on a body surface, form an open circuit and accordingly will not drain current from the DC power source (e.g., a battery) during storage.
On the other hand, the complex circuits utilized in more recent iontophoretic delivery devices require internal switches in order to disconnect the power source from the circuitry in order to prevent current drain during storage life. See, for example, Sibalis U.S. Pat. No. 4,808,152 (switch 80 in FIG. 2). Unfortunately, these devices need to be switched on at the time they are placed on the body in order to begin operating. This represents a potential opportunity for error in drug delivery because the physician, nurse and/or the patient may not remember to turn on the switch. In addition, in the case of a defective switch or a switch having poor electrical contact there may be uncertainty concerning whether or not the device is actually delivering the beneficial agent.
Accordingly, it is an object of the present invention to provide an electrical circuit which does not drain current from the power source until the device is placed in operation on the body.
It is a further object to provide such a circuit which does not require the use of manually operated switches which must be correctly engaged by either the patient, the physician and/or other medical technician.